The present invention is generally directed to a coating apparatus and method of coating articles, such as hollow cylindrical articles, for example, photoresponsive devices used in imaging apparatuses and the like applications. More specifically, the present invention relates to an improved coating apparatus and coating method for articles and which apparatus and method obviates or minimizes the need to conduct a so-called bottom-edge-wipe step or operation and which step is common in conventional coating apparatus and coating methods. The present invention provides coated articles with superior and unexpected coating properties, such as reduced or eliminated coating defects, such as bubbles entrapped in the resulting coated article.
In electrophotography, and particularly in xerographic copying machines, coated substrates such as photoreceptor belts or cylindrical photoreceptor drums are common. Photoreceptor embodiments include at least one coating of photoconductive material, which can be formed on the photoreceptor by known techniques such as immersion or dip coating.
The end regions of a coated photoreceptor are commonly used to either or both engage, for example, with flanges, the printer""s or copier""s drive mechanism and to support a developer housing. If the developer housing rides on the coated area at one end region of the drum, the coating composition can be rubbed-off and which rub-off particles can contaminate various components in the machine such as the cleaning system and any optical exposure systems employed in the machine. Also, the coating can interfere with devices or componentry that is designed to electrically ground the drum by merely riding on the outer surface at one end region of the drum. Thus, preferably both the outer and inner end regions of a photoreceptor generally must be free of the coating composition.
In dip coating, the upper end region of the photoreceptor drum might be kept free of coating composition by orienting the drum vertically and dipping the drum into a bath of coating composition to a predetermined depth which avoids coating the upper end region. However, the coating formed over the lower region end of the photoreceptor must still be removed, for example, by mechanically or manually wiping the lower end region or by applying solvents to it. This solvent removal procedure can be problematic since it may employ environmentally harmful solvents. Also, the coating removal procedure may require the use and maintenance of special equipment in the clean room which can increase activity in the clean room, thereby decreasing productivity. In addition, the coating removal procedure a clean room increases costs since the procedure must meet clean room requirements. Alternatively, the end regions of the photoreceptor drums may be masked to prevent coating of the end regions. However, the mask must be removed from the photoreceptor drum subsequent to the dip coating process which is disadvantageous since this involves an additional step. Consequently, there is a need, which the present invention addresses, for a coating method which eliminates or minimizes the above-identified problems.
Photoresponsive articles or devices are comprised generally of a transport layer and a photogenerator layer. These devices may include a wide variety of additional or supplemental layers or coating and which coatings can provide enhanced performance properties or adaptable configurational features to the resulting coated device. The photoresponsive devices of the present invention are useful, for example, as imaging members in various electrostatographic imaging systems, including those systems wherein electrostatic latent images are formed on the imaging member. Additionally, the photoresponsive devices of the present invention can be irradiated with light, for example, as generated by a known laser or other suitable light source, to accomplish, for example, latent image formation by, for example, charged area discharge (CAD) or dark area discharge (DAD) methodologies.
Numerous photoresponsive devices for electrostatographic imaging systems are known including selenium, selenium alloys, such as arsenic selenium alloys; layered inorganic photoresponsive, and layered organic photoresponsive devices. Examples of layered organic photoresponsive devices include those containing a charge transport layer and a charge generator layer, or alternatively a photogenerator layer. Thus, for example, an illustrative layered organic photoresponsive device can be comprised of a conductive substrate, overcoated with a charge generator layer, which in turn is overcoated with a charge transport layer, and an optional overcoat layer overcoated on the charge transport layer. In a further xe2x80x9cinvertedxe2x80x9d variation of this device, the charge transporter layer can be overcoated with the photogenerator layer or charge generator layer. Examples of generator layers that can be employed in these devices include, for example, charge generator materials such as pigments, selenium, cadmium sulfide, vanadyl phthalocyanine, x-metal free phthalocyanines, dispersed in binder resin, while examples of transport layers include dispersions of various diamines, reference for example, U.S. Pat. No. 4,265,990, the disclosure of which is incorporated herein by reference in its entirety.
There continues to be a need for improved photoresponsive devices, and improved methods and apparatus for making such devices. Additionally, there continues to be a need for methods and apparatus which reduce defects and provide improved performance properties of the resulting coated photoresponsive devices, and which devices are economical to prepare and can retain their properties over extended periods of time. Furthermore there continues to be a need for photoresponsive devices that permit both normal and reverse copying of black and white as well as full color images, especially in high speed digital printing systems.
In U.S. Pat. No. 5,683,742, to Herbert, et al., issued Nov. 4, 1997, there is disclosed a coating method for a substrate having an end region comprising: a) rubbing a non-wetting material across the end region to adhere the non-wetting material to the end region; and b) contacting a portion of the substrate including the end region with a coating composition, whereby the coating composition adheres to the substrate surface free of the non-wetting material and the non-wetting material minimizes adherence of the coating composition to the end region.
In U.S. Pat. No. 5,616,365, to Nealey, issued Apr. 1, 1997, there is disclosed a method for coating a substrate having an end region including: a) positioning the substrate within a coating vessel to define a space between the vessel and the substrate and providing a downwardly inclined surface contiguous to the outer surface at the end region of the substrate; b) filling at least a portion of the space with a coating solution; and c) withdrawing the coating solution from the space, thereby depositing a layer of the coating solution on the substrate.
In U.S. Pat. No. 5,693,372, to Mistrater et al., issued Dec. 2, 1997, there is disclosed a process for dip coating drums comprising providing a drum having an outer surface to be coated, an upper end and a lower end, providing at least one coating vessel having a bottom, an open top and a cylindrically shaped vertical interior wall having a diameter greater than the diameter of the drum, flowing liquid coating material from the bottom of the vessel to the top of the vessel, immersing the drum in the flowing liquid coating material while maintaining the axis of the drum in a vertical orientation, maintaining the outer surface of the drum in a concentric relationship with the vertical interior wall of the cylindrical coating vessel while the drum is immersed in the coating material, the outer surface of the drum being radially spaced from the vertical interior wall of the cylindrical coating vessel, maintaining laminar flow motion of the coating material as it passes between the outer surface of the drum and the vertical interior wall of the vessel, maintaining the radial spacing between the outer surface of the drum and the inner surface of the vessel between about 2 millimeters and about 9 millimeters, and withdrawing the drum from the coating vessel.
In U.S. Pat. No. 5,725,667, to Petropoulos et al., issued Mar., 10, 1998, there is disclosed a dip coating apparatus including: a) a single coating vessel capable s of containing a batch of substrates vertically positioned in the vessel, wherein there is absent vessel walls defining a separate compartment for each of the substrates; b) a coating solution disposed in the vessel, wherein the solution is comprised of materials employed in a photosensitive member and including a solvent that gives off a solvent vapor; and c) a solvent vapor uniformity control apparatus which minimizes any difference in solvent vapor concentration encountered by the batch of the substrates in the air adjacent the solution surface, thereby improving coating uniformity of the substrates.
In U.S. Pat. No. 5,820,897, to Chambers et al., issued Oct. 13, 1998, there is disclosed a method of holding and transporting a hollow flexible belt throughout a coating process. The method includes placing an expandable insert into the hollow portion of a seamless flexible belt, and expanding the insert until it forms a chucking device with a protrusion on at least one end. A mechanical handling device is then attached to the protrusion, and will be used to move the chuck and the belt through the dipping process, as materials needed to produce a photosensitive device are deposited onto the surface of the belt, allowing it to be transformed into an organic photoreceptor. The chucking device and flexible belt are then removed from the mechanical handling device, the belt is cut to the desired width, and the chuck is removed from the inside of the photoreceptor.
The aforementioned references are incorporated in their entirety by reference herein.
Embodiments of the present invention, include:
An apparatus comprising:
a tank with a closed base end and an open top end, and adapted to contain a coating formulation; and
a receiver member with at least a cone shape, where the base of the cone is attached to the interior and to the base end of the tank and adapted to receive an article for coating;
A coating method comprising:
press fitting an article for coating onto the base portion of the receiver member of the abovementioned coating apparatus; and
partially filling the tank with a coating solution;
removing the coating solution from the tank; and
removing the resulting coated article from the receiver member, wherein the interior of the article is free of residual coating solution.
An article comprising:
a conofrustum solid adapted for attachment within a coating vessel, where the solid is constructed of a partially compressible material, such as a closed cell foam or closed cell sponge, and adapted to receive and support an object for dip or immersion coating.
These and other embodiments of the present invention are illustrated herein.